Nowadays the information center typically includes many frames in each of which a plurality of servers or uninterrupted power systems (UPS) are horizontally stacked from up to down. In order to distribute power to each server and UPS within the frame, power distribution units (PDUs) which are generally configured to provide multiple sockets similar to those in the household plug board are assembled into the frame vertically or horizontally. Since there is no standard for the vertical distances between the mounting apertures in the frame, various installation systems for the PDU of rail-sliding rack type are provided in the prior art.
US application publication No. US20020022406A1 discloses a conventional installation system for the PDU of rail-sliding rack type, comprising a rail structure or a rail member arranged on the back surface or bottom cover of the PDU, and a sliding rack cooperated with the rail structure, wherein the sliding rack can be assembled into a frame and the rail structure may press fit into the sliding rack, so as to realize the installation of the PDU. In the above-mentioned installation system, the PDU is retained in relation to the frame mainly by means of the contacting friction between the rail structure and the sliding rack. Such installation system has a drawback that the PDU may slide down or even fall down relative to the sliding rack and thus the frame, when the PDU product is relatively heavy or encounters a greater external force in vertical direction.
The co-pending Chinese patent application No. CN201110459201.4 assigned to the assignee of the present application provides a retaining element for stopping the relative movement between the rail member and the sliding rack. The rail member at its bottom has a longitudinally extending groove. The retaining element comprises a body extending transversely along the sliding rack and having a side surface for abutting against the sliding rack and two ends opposed to each other in the transverse direction, with one of the ends having a catch portion which press fits with a first side surface and a second side surface of the groove, and the other end of the body opposed to the catch portion as a free end. The catch portion is provided with a protrusion, as a balance pivot, for pressing the latch portion into or removing it from the groove by means of the free end. In the event that the PDU slides due to an accident such as earthquake, the PDU may be effectively stopped so as not to further slide down or fall down by means of the tool-free retaining element.
In the CN patent application, a groove formed on the bottom surface (i.e. the backside facing the rail rack or frame) of the housing of the PDU (or rail member) is required for the retaining element for PDU, which restricts the range of applications. For example, the retaining element is not suitable for the PDU without a groove formed on the backside of the housing, e.g., the power distribution system disclosed in the GB patent GB2292489B assigned to the applicant of this application. Moreover, providing a groove at the bottom surface of the housing will adversely increase the thickness of the PDU increases, which contradicts with the current tendency of providing a PDU as compact as possible.